Exercise 1: First Terra Draw Implementation

Let's create a basic Terra Draw setup with MapLibre GL JS — without any UI interaction yet.

Try it in the live editor

The starter code below contains two TODO comments. Complete them, then click Run ▶. If you get stuck, open the Answer tab.

Live editor — open this page in the browser to run the code.

Walkthrough

First, import Terra Draw and the MapLibre adapter:

import { TerraDraw, TerraDrawRectangleMode } from 'terra-draw';
import { TerraDrawMapLibreGLAdapter } from 'terra-draw-maplibre-gl-adapter';

Then create a Terra Draw instance, connecting the map through the adapter and registering the rectangle mode:

const draw = new TerraDraw({
    // Using the MapLibre Adapter
    adapter: new TerraDrawMapLibreGLAdapter({ map }),

    // Add the Rectangle Mode
    modes: [new TerraDrawRectangleMode()],
});

Finally, wait for MapLibre to load the map style, then start drawing:

// Have to wait for MapLibre to load the map style before starting to draw
map.once('load', () => {
    // Start drawing
    draw.start();
    draw.setMode("rectangle");
});

Now you can draw rectangle polygons by clicking on the map: one click starts the rectangle, a second click finishes it.

In the local SvelteKit template

Open src/routes/+page.svelte, add the imports below the existing ones, and put the Terra Draw setup at the end of the onMount() function, after the map initialization:

onMount(() => {
    // ... existing map initialization ...

    const draw = new TerraDraw({
        adapter: new TerraDrawMapLibreGLAdapter({ map }),
        modes: [new TerraDrawRectangleMode()],
    });

    map.once('load', () => {
        draw.start();
        draw.setMode("rectangle");
    });
});

Testing Your Implementation

1. Save your changes and the Vite development server should automatically reload
2. Open your browser to http://localhost:5173
3. Test drawing - click on the map to create rectangles

What's Next?

Now that you have a working Terra Draw implementation without UI, let's add more Terra Draw modes with UI buttons.

Continue to Exercise 2